Cigarette smoking is a pre-eminent public health problem, recognized as early as 1965. The rapid acquisition and addiction to cigarettes during adolescence is at the root of this continuing epidemic. A cardinal feature of smoking is the high level of individual variation in susceptibility to acquiring the habit;44% of this vulnerability to initiate smoking is attributed to genetics. Identifying differences in gene expression within phenotype- specific neurons that control and respond to the reinforcing properties of nicotine, across 5 adolescent inbred strains of rats and 10 F1 isogenic crosses, will provide novel and fundamental insight into this variation in susceptibility. We will exploit sophisticated, but well established rat models with a high level of genetic and phenotypic variation, cutting- edge expression approaches (laser-capture microdissection, array and RNA-seq analysis), and innovative bioinformatic resources developed by our groups (primarily Chilibot and GeneNetwork). A two-year grant is perfectly suited to our design. SA 1 will identify, analyze and confirm Signature Genes characteristic of phenotype-specific neurons (e.g., ventral tegmental dopamine neurons projecting to accumbal shell), combining retrograde tracing, immunocytochemistry, laser capture microdissection and analysis of gene expression arrays in Lewis and Fisher344 rats. In SA 2, clusters of associated transcripts, identified statistically from transcriptomes of heterogenous tissue sections (e.g., ventral tegmentum), will be associated with phenotype-specific neurons, using the Signature Gene sets. Those transcripts that covary with acquisition of nicotine self-administration across all inbred rat strains and F1 crosses are Candidate Genes. These are highly likely to participate in determining strain-dependent differences in the function of these specific neurons, which in turn contribute to variation in the acquisition of nicotine SA across strains. SA 3 will predict nicotine acquisition behavior from the expression of Candidate Genes in adolescent HXB recombinant inbred rats. This project will broadly impact the field by developing foundational models and predictions with general applicability, regarding genetic and expression differences that contribute to differences in the likelihood of initiating and acquiring cigarette smoking. PUBLIC HEALTH RELEVANCE: Habitual cigarette smoking is a major public health problem that is resistant to treatment. Individuals usually become smokers during adolescence, and the likelihood of developing this habit varies from individual to individual. Genetic factors play a large role in determining who will become a chronic smoker during adolescence. This research will identify these genetic factors, providing the foundation for new smoking prevention strategies.